dick, gumshoe, hawkshaw - someone who is a detective

plainclothesman - a detective who wears civilian clothes on duty

police officer, policeman, officer - a member of a police force; "it was an accident, officer"

tracer - an investigator who is employed to find missing persons or missing goods

investigator - someone who investigates

private detective, private eye, private investigator, shamus, sherlock, operative, PI - someone who can be employed as a detective to collect information

sleuth, sleuthhound - a detective who follows a trail